Persistent organic pollutant refers to hydrophobic organic substance of high toxicity which remains, migrates in the environment for a long time, and accumulates in organism, the persistent organic pollutant is mainly remained in organic phase of sediment in natural environment, so that, the pollutant concentration in sediment pore water is higher than that in the water, Meanwhile, the persistent organic pollutant constantly diffuses to overlaying water and cycles in the ecological system through evaporation, dissolution, adsorption and organism absorption etc. A correct assessment of the exchange flux of the hydrophobic pollutant between the sediment pore water and the overlaying water is highly necessary since the hydrophobic organic substance is potentially harmful to the organism.
In the prior art, the traditional method is to measure the concentration of the organic substance in the sediment and water respectively, and then make a comparison and estimates the diffusion direction and flux of the organic pollutant.
Alternatively, a method for measuring flux in situ is adopted, in which, a flux test box is arranged in situ and the content of the target substance in the adsorbent within the test box is measured after a period of time according to the passive diffusion principle, and then the diffusion flux is estimated according to an balanced partition coefficient.
In the prior art, though the traditional method is simple, convenient and direct, it has the following disadvantages: first, it can only determine data of single point of pore water and overlaying water and is hard to exactly reflect the characteristics of the concentration change; second, the estimation of the interface flux is based on the hypothesis that the concentration gradient is linear, which does not accord with the theoretical calculation and the actual situation; third, the measurement of the concentration of the organic substance in the sediment pore water and the overlaying water needs a lot of solvate, the recycle rate is low, and the analysis cost is too high.
The method for measuring flux in situ has the advantages of direct diffusion flux measurement and little interference from the environment. However, it also has the following disadvantages: first, the method is to measure a static unidirectional diffusion flux, namely, under the drive of the adsorption of adsorbent, the escaped flux of migration of part of target substance from the sediment or the overlaying water excludes the flux that target substance deposited downward in water, and therefore the outcome is not the balanced flux; second, the flux measured is that in position of the adsorbent other than the complete diffusion flux from the sediment to the water; third, only a single data of at certain depth of the water can be measured.